Processes and apparatuses for the continuous casting of metal bar are well known in the art. A continuous casting apparatus typically comprises an internally and externally cooled casting wheel having a center about which it rotates. The wheel has a continuous groove about its periphery which serves as one part of a molding cavity. The apparatus additionally comprises an endless belt which is positioned to be in close contact with the periphery of the wheel during a segment of its rotation, thereby forming a molding cavity. Molten metal is continuously cast into the cavity formed between the rotating wheel and the moving belt. As the metal contained in the cavity formed between the wheel and the belt rotates with the wheel angularly about its center, heat is removed from the metal and a solidified bar is formed. The bar is removed from the rotating wheel and directed to mills for further processing.
The metals which are typically cast in a continuous casting system are metals which are malleable ductile and easily formable by rolling into rod such as aluminum and copper.
As the cast bar is discharged from the wheel, it is typically rolled while still at a temperature within a conventional hot-working temperature range. In the rolling process, the overall longitudinal and transverse dimensions (cross-sectional area) of the bar are reduced in stages by passing through successive conventional rolling mill stands, until a round rod having the desired diameter is produced. The bar length increases accordingly as the cross-sectional area is reduced. Rolling mill stands conventionally comprise machines having grooved rolls which are mechanically loaded. The grooved rollers size the bar and pull it through the rolling mill.
Since the bar comes off of the casting wheel at a relatively slow translational speed, and since the translational speed of the bar increases with each successive size reduction, the bar is preferably under a tensile load during the rolling process. If there is a break in the bar after it comes off the wheel, the bar on the distal side of the break will continue to move through the rolling mill stands due to the action of the mill rolls. It is known, however, that the corresponding loss of tension caused by the bar break results in excess metal being pushed to the outside of the bar or rod. This metal takes the form of protuberances or fins on the side of the rod as it exits from the last mill stand.
When circular rod is produced by a continuous casting and rolling system, it is desirable to test the rod for surface defects prior to coiling. The rod produced by continuous casting and rolling processes is typically used in high speed wire drawing manufacturing processes where it is drawn at high speed through dies to produce fine diameter wires such as magnet wire. It is known that surface defects in the rod will produce defective or inferior wire.
It is known in the art that defects in rod can be detected by an eddy current detector. An eddy current detector is an electrical device producing a magnetic field thereby inducing currents in metal rod passing therethrough. The detector typically has a hollow cylindrical frame through which the rod passes. Irregularities in the rod produce abnormal eddy currents which are detected and correlated to defects. The clearance between the sidewalls of the detector and the rod is mechanically close so that extreme projections or deformities of the rod will damage the detector. This situation occurs when a continuous rod breaks thereby resulting in fins on the rod.
Continuous casting apparatuses are disclosed in U.S. Pat. Nos. 3,279,000 and 3,682,234, the disclosures of which are incorporated by reference.
A method and apparatus for the detection of eddy current impeding flaws in moving electrically conductive objects such as rod is disclosed in U.S. Pat. No. 3,881,151. Sensing coils in the apparatus measure changes in eddy currents induced by magnetic fields signifying flaws in rod passing through the detector. The flaws can comprise voids, ferrous inclusions, breaks, cracks, etc.
U.S. Pat. No. 3,552,161 discloses a method of protecting a mill from rod irregularities in a continuous casting process. A sensing means energizes a cutting device which severs the rod and diverts it before it can enter and possibly damage a mill.
U.S. Pat. No. 3,731,512 discloses a means for severing a defective rod or bar in a rolling mill to prevent the bar from being further processed.
Eddy current detectors are expensive and it is not practical to have numerous spares. When spares are not available, the process must be run without eddy current detectors. The rod produced is then of unknown surface quality and may not be suitable for use in certain high speed wire drawing applications.
Accordingly, what is needed in this art is a method of manufacturing rod in a continuous casting and rolling process so that an eddy current detector used in the process will be protected against damage when there is a rod break in the continuous rod or bar during the processing.